On the feasibility of compressing CO{sub}2 as working fluid in scroll compressors

摘要

A theoretical analysis of compressing CO{sub}2 gas (R-744) in an open scroll machine for automotive air conditioner has been carried out. A R-134a scroll compressor with swept volume of 80 cm{sup}3 i.e. for mediumed-size car was applied as abaseline compressor. The focus has been on overall geometrical dimensions, weight of moving parts and to quantify the gas leakage. The objective was to achieve competitive parameter values for the R-744. It was applied two different set of R-744 scrollprofiles. One scroll set with maximum 3 pairs of compression pockets and one set with maximum 2 pairs. Maximum 2 pairs was also the case for the R- 1 34a compressor.The total weight of the moving parts and overall dimensions was fulfilled compared to the R- 134a scroll for the R-744 scroll set with maximum 2 pairs of compression pockets but not for the R-744 scroll set with 3 pairs. The volumetric- and the isentropic efficiency based only on gas leakage loss without influence of lubricant was lower for both R-744 scroll set at equal clearance gap. Equal volumetric- and isentropic efficiency could be obtained when the clearance gap was 56 and 67% respectively comparedto the R-134a compressor. This was the case at both 1000 rpm (idle condition) and 2500 (driving condition). A self-adjusting back pressure mechanism must be applied in order counteract the larger thrust/axial force in the R-744 compressor.